greptile P2 nitpick: the previous commit's docblock said "on every
PreToolUse hook" but the module header (and the actual hook wiring
in `hooks/hooks.json`) identifies this script as a PostToolUse
hook — it runs *after* each tool invocation to update the running
session aggregate. One-word typo, no behavior change.
coderabbitai flagged: the two `catch` blocks in `readSessionCost`
silently swallowed every failure mode. A malformed `costs.jsonl`
row, a permission error opening the file, or any other unexpected
I/O failure would silently return zero cost — masking real
problems and feeding stale or zero numbers into
`ecc-context-monitor.js` (which then injects them as
`additionalContext` into the live model turn).
Fix two things, both fail-open-preserving:
1. **Inner JSON.parse catch** — count malformed lines and write
one aggregated breadcrumb per call:
[ecc-metrics-bridge] skipped N malformed line(s) in <path>
Aggregating (rather than per-line) keeps a log-flooded
`costs.jsonl` diagnosable without overwhelming stderr.
2. **Outer fs.readFileSync catch** — write a breadcrumb on real
errors, but stay silent on `ENOENT`. The "no costs.jsonl yet"
case is genuinely normal (no Stop event has fired this session)
and producing noise on every PreToolUse before the first Stop
would be reviewer-visible spam. All other error codes
(`EACCES`, `EISDIR`, `EMFILE`, …) get:
[ecc-metrics-bridge] failing open after <name> reading <path>: <msg>
In both cases the function still returns the zero-cost fallback
so the bridge never breaks tool execution — only the
diagnosability changes.
Two new regression tests in
`tests/hooks/ecc-metrics-bridge.test.js`:
✓ readSessionCost writes a stderr breadcrumb when malformed
lines are skipped — feeds 4 rows (2 valid, 2 malformed),
asserts the last valid row still wins AND captured stderr
contains "skipped 2 malformed line(s)".
✓ readSessionCost stays silent when costs.jsonl does not exist
(ENOENT) — uses a fresh tmp HOME with no metrics dir, asserts
zero return AND empty stderr.
Test count: 16 → 18; `npm test` green; `yarn lint` clean.
`readSessionCost` read only the trailing 8 KiB of
`~/.claude/metrics/costs.jsonl` to "avoid scanning entire file".
That ceiling is the opposite-sign sibling of the double-count bug
fixed in the previous commit: once a session's most recent
cumulative row gets pushed past the 8 KiB window by newer rows
from other sessions, the bridge silently reports `totalCost: 0`,
`totalIn: 0`, `totalOut: 0` for that session — same false signal
to `ecc-context-monitor.js`, same wrong number injected into the
live model turn as `additionalContext`.
`cost-tracker.js` has no rotation policy, so on any non-trivial
workstation costs.jsonl grows past 8 KiB within minutes of normal
use. For users who keep multiple concurrent sessions, this means
the second-and-later sessions silently report zero almost
immediately.
Reproduced before this commit:
$ HOME=/tmp/eccc node -e '
const fs = require("fs");
const m = require("./scripts/hooks/ecc-metrics-bridge.js");
// S1 row at file start, then 200 rows of OTHER-session noise (~16 KiB).
// S1 is the row we want, but it sits past the 8 KiB tail.
const s1 = `{"session_id":"S1","estimated_cost_usd":0.5,"input_tokens":500,"output_tokens":250}`;
const other = `{"session_id":"OTHER","estimated_cost_usd":1,"input_tokens":100,"output_tokens":50}`;
fs.mkdirSync("/tmp/eccc/.claude/metrics", { recursive: true });
fs.writeFileSync("/tmp/eccc/.claude/metrics/costs.jsonl",
[s1, ...Array(200).fill(other)].join("\\n") + "\\n");
console.log(JSON.stringify(m.readSessionCost("S1")));'
{"totalCost":0,"totalIn":0,"totalOut":0}
Expected: `{"totalCost":0.5, "totalIn":500, "totalOut":250}` (the
S1 row that exists in the file).
Actual: zero — the row is past the 8 KiB tail.
Fix: drop the `fs.openSync` + bounded `fs.readSync` + position
arithmetic in favour of `fs.readFileSync(costsPath, 'utf8')` and
iterate every line. Each row is ~150 bytes; even 100k rows is
~15 MB and a single sync read on PreToolUse is in the low ms.
If file rotation lands in `cost-tracker.js` later, this scan
becomes proportionally cheaper.
After this commit the reproduction above returns
`{"totalCost":0.5, "totalIn":500, "totalOut":250}`.
Regression test in `tests/hooks/ecc-metrics-bridge.test.js`:
`readSessionCost finds session row beyond the old 8 KiB tail
boundary`. The test asserts the costs.jsonl fixture is > 8 KiB
before reading so any reintroduction of a bounded tail would
re-fail the test (i.e. the assertion is the contract, not the
specific number 8192).
Together with the previous commit, both directions of the
metrics-bridge cost-reporting bug are closed.
`ecc-metrics-bridge.js#readSessionCost` summed the
`estimated_cost_usd`, `input_tokens`, and `output_tokens` of
every matching row in `~/.claude/metrics/costs.jsonl`. That breaks
the documented contract of `scripts/hooks/cost-tracker.js`, which
explicitly states (in its module docblock):
Cumulative behavior: Stop fires per assistant response, not
per session. Each row therefore represents the cumulative
session total up to that point. To get per-session cost, take
the last row per session_id.
Summing N cumulative rows over-counts by roughly (N+1)/2 ×. For a
session with 3 rows at 0.01, 0.02, 0.03 USD (true running total
0.03), the bridge today reports 0.06 USD. The over-counted value
feeds `ecc-context-monitor.js`, which then trips its
COST_NOTICE_USD / COST_WARNING_USD / COST_CRITICAL_USD thresholds
on phantom spend AND injects the inflated number as
`additionalContext` into the live model turn — so the agent
itself is told a wrong cost.
Reproduced on `main` before this commit:
$ cat > /tmp/eccc/.claude/metrics/costs.jsonl <<EOF
{"session_id":"S1","estimated_cost_usd":0.01,"input_tokens":333,"output_tokens":166}
{"session_id":"S1","estimated_cost_usd":0.02,"input_tokens":666,"output_tokens":333}
{"session_id":"S1","estimated_cost_usd":0.03,"input_tokens":1000,"output_tokens":500}
EOF
$ HOME=/tmp/eccc node -e 'const m = require("./scripts/hooks/ecc-metrics-bridge.js"); \
console.log(JSON.stringify(m.readSessionCost("S1")))'
{"totalCost":0.06,"totalIn":1999,"totalOut":999}
Expected: `{"totalCost":0.03,"totalIn":1000,"totalOut":500}` (the
last cumulative row).
Actual: 2× over-count.
Fix: replace `+=` with `=` in the matching branch so the assigned
values reflect the most recent row encountered. The iteration
order is file order, which is also event time order, so the last
assignment wins — exactly the contract cost-tracker writes
against.
After this commit the reproduction above returns
`{"totalCost":0.03,"totalIn":1000,"totalOut":500}`.
Regression test in `tests/hooks/ecc-metrics-bridge.test.js`:
`readSessionCost returns the LAST cumulative row, not the sum
(cost-tracker contract)`. The existing
`readSessionCost does not include unrelated default-session rows`
test happened to pass even with the bug because it only had one
target-session row — single-row sessions are coincidentally
correct under both formulas. The new test uses three rows so the
two formulas diverge.
A second issue in the same function — the 8 KiB tail-only read
silently drops older rows once a session's recent cumulative
totals scroll past that window — is fixed in the next commit.
Salvages the useful statusline/context monitor work from stale PR #1504 while preserving the current continuous-learning hook runner wiring.
Adds the metrics bridge, context monitor, statusline script, shared cost/session bridge utilities, and tests. Fixes the reviewed false loop-detection hash collision for non-file tools, avoids default-session cost inflation, sanitizes statusline task lookup, and records hook payload session IDs in cost-tracker.
